Field of the Invention
The present invention relates to a method for pretreatment of biological samples containing enantiomers of lenalidomide, wherein deproteinization is carried out under acidic conditions, and to a method for quantifying enantiomers of lenalidomide in a biological sample, wherein a biological sample containing enantiomers of lenalidomide, pretreated in such a manner, is analyzed by high-performance liquid chromatography.
Related Background Art
Lenalidomide, a derivative of thalidomide, is widely used as an effective immunomodulating drug for different malignant blood diseases such as multiple myeloma. Lenalidomide has been reported to have a superior toxicity profile and more excellent immunomodulatory activity compared to thalidomide (NPL 1). The pharmacokinetic properties of lenalidomide have been elucidated by HPLC methods in reversed-phase mode (NPL 2, NPL 3 and NPL 4), and the final excretion half-life of lenalidomide is conjectured to be about 3 to 4 hours.
In regard to thalidomide and its derivatives and analogs, differences in drug activity have been reported between the R-form and S-form. For example, the sedative action of thalidomide has only been reported with the R-form, (NPL 5), while S-pomalidomide (3-amino-phthalimide-glutarimide) has been reported to significantly inhibit corneal vascularization elicited by bFGF or VEGF, compared to the R-form or racemic form (NPL 6).
Despite such differences in activity between the enantiomers, thalidomide is still administered as a racemic mixture with R-form:S-form=50:50. One of the main reasons for this is its property of very rapid racemization in blood (NPL 7).
The enantiomers of thalidomide have been separated and quantified by repeated extraction using organic solvents, or by chromatographic methods using an enantioselective stationary phase such as modified amylose (NPL 8), cellulose (NPL 7), vancomycin (NPL 9) or methacrylamide (NPL 10), and it has been shown that racemization is very rapid in the blood. Such racemization was first disclosed by G. Blaschke et al., who reported that the racemization half-life of thalidomide in human blood plasma is approximately 10 minutes (NPL 10). This is extremely short considering that the excretion half-life of thalidomide is 8.7 hours (NPL 11).
Because it has such pharmacokinetic properties, it is thought that there is no pharmacological significance in administering a pure enantiomer of thalidomide, and it has been assumed that lenalidomide, which has a basic backbone similar to thalidomide, would also have similar properties. Therefore, the pharmacokinetic and pharmacological properties of the pure enantiomers of lenalidomide have not been thoroughly researched, and absolutely no data has been reported on separation and quantification of pure enantiomers of lenalidomide in biological samples.